In the related art, in order to assist safe driving of a vehicle, a vehicle-mounted device is known that issues warnings when a driver is not attentive. For example, Patent Literature 1 disclosed a technique that sets warning levels based on at least one of the geographical circumstances around the subject vehicle position, vehicle circumstances around the subject vehicle, and driving circumstances of the subject vehicle and warns of driver inattentiveness based on the set warning levels when driver inattentiveness is detected.